Optical fiber strain measuring method and optical fiber strain measuring device

Abstract

The present disclosure relates to an optical fiber strain measurement method including, in order: a strain amount measurement step S 2 of measuring a strain amount ε n ′ of each core wire of an optical fiber ribbon F; a torsion angle calculation step S 3 of calculating a torsion angle γ per unit length of the optical fiber ribbon F on the basis of a difference ε′ in strain amount between an outer core wire and an inner core wire; a torsional strain amount calculation step S 4 of calculating a strain amount ε n caused by torsion of each core wire of the optical fiber ribbon F on the basis of the torsion angle γ; and a tensile strain amount calculation step S 5 of subtracting the strain amount ε n from the strain amount ε n ′, and calculating a strain amount Δε n caused by tension of each core wire of the optical fiber ribbon F.

The invention claimed is: 
     
         1 . An optical fiber strain measurement method comprising, in order:
 by processing circuitry, measuring a strain amount of each core wire of an optical fiber ribbon using a Brillouin-optical time domain reflectometer (B-OTDR) or an optical frequency domain reflectometer (OFDR);   by the processing circuitry, calculating a torsion angle per unit length of the optical fiber ribbon, based on a difference in strain amount between an outer core wire and an inner core wire of the optical fiber ribbon;   by the processing circuitry, calculating a strain amount caused by torsion of each core wire of the optical fiber ribbon, based on the torsion angle per unit length of the optical fiber ribbon; and   by the processing circuitry, subtracting the strain amount caused by torsion of each core wire of the optical fiber ribbon from the strain amount of each core wire of the optical fiber ribbon measured in the strain amount measurement step, and calculating a tensile strain amount caused by tension of each core wire of the optical fiber ribbon when the strain by torsion is caused in all core wires of the optical fiber ribbon.   
     
     
         2 . The optical fiber strain measurement method according to  claim 1 , wherein calculating the torsion angle includes calculating the torsion angle per unit length of the optical fiber ribbon without taking an effect of tension of each core wire of the optical fiber ribbon into account. 
     
     
         3 . The optical fiber strain measurement method according to  claim 1 , wherein calculating the tensile strain amount includes calculating the strain amount caused by tension of each core wire of the optical fiber ribbon without taking an effect of torsion of each core wire of the optical fiber ribbon into account. 
     
     
         4 . The optical fiber strain measurement method according to  claim 1 , further comprising, subsequently, by the processing circuitry, calculating strain amounts caused by torsion and tension of a structure in which the optical fiber ribbon is installed, based on the strain amounts caused by the torsion and the tension of each core wire of the optical fiber ribbon, respectively. 
     
     
         5 . An optical fiber strain measurement device comprising: processing circuitry configured to:
 to measure a strain amount of each core wire of an optical fiber ribbon using a Brillouin-optical time domain reflectometer (B-OTDR) or an optical frequency domain reflectometer (OFDR);   calculate a torsion angle per unit length of the optical fiber ribbon, based on a difference in strain amount between an outer core wire and an inner core wire of the optical fiber ribbon;   calculate a strain amount caused by torsion of each core wire of the optical fiber ribbon, based on the torsion angle per unit length of the optical fiber ribbon; and   subtract the strain amount caused by torsion of each core wire of the optical fiber ribbon from the strain amount of each core wire of the optical fiber ribbon measured, and calculate a tensile strain amount caused by tension of each core wire of the optical fiber ribbon when the strain by torsion is caused in all core wires of the optical fiber ribbon.   
     
     
         6 . The optical fiber strain measurement device according to  claim 5 , wherein the processing circuitry is configured to calculate the torsion angle per unit length of the optical fiber ribbon without taking an effect of tension of each core wire of the optical fiber ribbon into account. 
     
     
         7 . The optical fiber strain measurement device according to  claim 5 , wherein processing circuitry is configured to calculate the tensile strain amount caused by tension of each core wire of the optical fiber ribbon without taking an effect of torsion of each core wire of the optical fiber ribbon into account. 
     
     
         8 . The optical fiber strain measurement device according to  claim 5 , wherein the processing circuitry is further configured to calculate strain amounts caused by torsion and tension of a structure in which the optical fiber ribbon is installed, based on the strain amounts caused by the torsion and the tension of each core wire of the optical fiber ribbon, respectively.